1. Field of the Invention
The present invention relates to an automatic automotive transmission and more specifically to an orifice control arrangement for such a transmission.
2. Description of the Prior Art
JP-A-60-81550 disclose an automatic automotive transmission which includes a gear train having two planetary gear seats; a plurality of friction elements in the form of clutches and brakes via which the gear train can be conditioned to produce a plurality of different gear ratios; and a control circuit via which the friction elements are selective engaged and released to produce the different gear ratios.
When this transmission is conditioned to produce D range operation, during first to third speeds a low clutch is engaged, while in third and fourth speeds a high clutch is engaged. In second and fourth speeds a band brake is engaged.
In order to engage the band brake in second speed, pressure is supplied to an apply chamber of the servo which operates the same. When third speed is required, line pressure is supplied to a release chamber of the servo in order to release the brake. Upon a 3-4 shift taking place, the pressure which is supplied to the release chamber is drained in a manner to permit the pressure which is being supplied to apply chamber to reapply the brake.
However, the control system which controls the supply of line pressure to the above mentioned chambers includes a 4-3 timing valve which is located in the circuit via which the low clutch is drained. This valve is such that during a 4-3 downshift at a vehicle speed above a predetermined limit the engagement of the lower clutch is delayed in order to smooth the shifting operation. A 3-2 timing valve is disposed in the conduit via which the release chamber of the above mentioned band brake servo is drained and delays the engagement of the band brake when a 3-2 downshift takes place above a given speed.
A select timing valve is disposed in the same circuit as the 4-3 timing valve and arranged upstream thereof. When a N-D select is made this valve reduces the rate at which the low clutch is engaged so as to attenuate select shock.
It should be noted that the 4-3 and 3-2 timing valves and the select timing valve take the form of orifice valves which selectively open and close by-pass passages which lead around fixed orifices. When these valves close the respective by-pass passages, the supply of line pressure to the respective friction elements is forced to pass through the fixed orifices and the friction element actuation pressure build up is delayed.
However, with this arrangement the 4-3 timing valve, the 3-2 timing valve and the select timing valve are independently supplied with and operated by the governor and second range pressures. Accordingly, in order to incorporate the above mentioned valves into the valve body of the control arrangement requires a number of independent valve bores and conduits.
This increases the complexity, weight and cost of the system.